Defect mitigation for recoating systems for additive manufacturing

ABSTRACT

Disclosed embodiments relate to recoater systems for use with additive manufacturing systems. A recoater assembly may be used to deposit a material layer onto a build surface of an additive manufacturing system. In some instances, the recoater assembly may include a powder entrainment system that trails behind a recoater blade of the recoater assembly relative to a direction of motion of the recoater blade across a build surface of the additive manufacturing system. The powder entrainment system may generate a flow of fluid across a portion of the build surface behind the recoater blade that at least temporarily entrains powder above a threshold height from the build surface to mitigate, or prevent, the formation of defects on the build surface with heights greater than the threshold height.

CROSS REFERENCE TO RELATED APPLICATIONS

This Divisional application claims the benefit of priority under 35U.S.C. § 121 to U.S. Application Serial No. 17/461,077, filed Aug. 30,2021, which claims the benefit of priority under 35 U.S.C. § 119(e) toU.S. Provisional Application Serial No. 63/074,752, filed Sep. 4, 2020,the disclosure of which is incorporated herein by reference in itsentirety.

FIELD

Disclosed embodiments are related to defect mitigation for recoatingsystems for additive manufacturing.

BACKGROUND

Additive manufacturing systems employ various techniques to createthree-dimensional objects from two-dimensional layers. After a layer ofprecursor material is deposited onto a build surface, a portion of thelayer may be fused through exposure to one or more energy sources tocreate a desired two-dimensional geometry of solidified material withinthe layer. Next, the build surface may be indexed, and another layer ofprecursor material may be deposited. For example, in conventionalsystems, the build surface may be indexed downwardly by a distancecorresponding to a thickness of a layer. This process may be repeatedlayer-by-layer to fuse many two-dimensional layers into athree-dimensional object.

Some additive manufacturing systems may include a system for depositingand/or spreading a precursor material onto a build surface. For example,in powder bed fusion systems, a recoater assembly may be used to deposita layer of powder onto the build surface. A recoater assembly mayinclude a recoater blade connected to a recoater support structure,which may be controlled so as to drag the recoater blade across thebuild surface, smoothing the deposited powder to provide a layer ofuniform thickness.

SUMMARY

In one embodiment, a recoater assembly for an additive manufacturingsystem includes a recoater blade and a powder entrainment system. Thepowder entrainment system may be configured to generate a flow of fluid,such as a gas, across a portion of the build surface with a velocityprofile that increases from the build surface towards the powderentrainment system. Additionally, in some optional embodiments, thepowder entrainment system may also be configured to trail behind therecoater blade relative to a direction of travel of the recoater bladeacross the build surface such that the powder entrainment systemgenerates the flow of fluid behind the recoater blade relative to thedirection of travel.

In one embodiment, a recoater assembly for an additive manufacturingsystem includes a recoater blade and a powder entrainment system. Thepowder entrainment system may be configured to trail behind the recoaterblade relative to a direction of motion of the recoater blade across abuild surface of the additive manufacturing system. The powderentrainment system may also include a moveable surface that isconfigured to move relative to a proximate portion of the build surfaceat a first velocity that is different from a second velocity of therecoater blade relative to the build surface. The first velocity isbetween or equal to 0.1 meters per second (m/s) and 2.0 m/s, and atleast a portion of the moveable surface is disposed at a height from thebuild surface that is between or equal to 0.5 millimeters (mm) and 10.0mm.

In one embodiment, a method of recoating a build surface of an additivemanufacturing system includes: depositing powder onto the build surfacewith a recoater assembly; and flowing a fluid across at least a portionof the build surface with a velocity profile that increases withincreasing distance from the build surface such that powder above athreshold height from the build surface becomes entrained in the flow offluid. Optionally, in some embodiments, flowing the fluid across thebuild surface includes flowing the fluid across the build surface behinda path of travel of the recoater blade.

It should be appreciated that the foregoing concepts, and additionalconcepts discussed below, may be arranged in any suitable combination,as the present disclosure is not limited in this respect. Further, otheradvantages and novel features of the present disclosure will becomeapparent from the following detailed description of various non-limitingembodiments when considered in conjunction with the accompanyingfigures.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In thedrawings, each identical or nearly identical component that isillustrated in various figures may be represented by a like numeral. Forpurposes of clarity, not every component may be labeled in everydrawing. In the drawings:

FIGS. 1A-1E depict a schematic cross-sectional view of one embodiment ofa defect growing in size during the deposition and fusion of subsequentlayers during an additive manufacturing process;

FIG. 2A is a schematic top view of a recoater blade moving towards adefect present on a build surface during deposition of a powder layer;

FIGS. 2B-2D are schematic top views of powder disturbances formed due tocontact of the recoater blade with the defect located on the buildsurface;

FIG. 3 is a schematic side view of an additive manufacturing systemaccording to one embodiment;

FIG. 4 is a schematic perspective view of an additive manufacturingsystem according to one embodiment;

FIG. 5 is a schematic side view of one embodiment of a recoater assemblyincluding a powder entrainment system during a recoating process;

FIG. 6 is a schematic side view of a rotating cylinder and theassociated velocity profile of the attached boundary layer of fluid;

FIG. 7 is a schematic side view of one embodiment of a rotating cylinderused to entrain powder above a threshold height from an associated buildsurface;

FIG. 8 is a schematic side view of one embodiment of a rotating cylinderincluding surface features formed on the cylinder;

FIG. 9 is a schematic diagram of the net velocity profile of a boundarylayer when a portion of a movable surface moves in a direction oppositea direction of motion of the overall assembly;

FIG. 10 is a schematic diagram of the net velocity profile of a boundarylayer when a portion of a movable surface moves in the same direction asa direction of motion of the overall assembly;

FIG. 11 is a schematic cross-sectional view of a rotating cylinder witha mask disposed on the leading portion of the cylinder;

FIG. 12 is a schematic cross-sectional view of a rotating cylinder witha mask disposed on both a leading and trailing portion of the rotatingcylinder;

FIG. 13 is a schematic cross-sectional view of a rotating cylinder witha mask on a trailing portion of the rotating cylinder and a vacuum port;

FIG. 14 is a schematic perspective view of one embodiment of a recoaterassembly including a plurality of rotating disks;

FIG. 15 is a schematic top view of one embodiment of a recoater assemblyincluding a plurality of rotating disks arranged in a linear array;

FIG. 16 is a schematic top view of one embodiment of a recoater assemblyincluding a plurality of rotating disks arranged in a staggered array;

FIG. 17 is a schematic cross-sectional view of a recoater assemblyincluding a belt according to one embodiment; and

FIG. 18 is a schematic cross-sectional view of a recoater assemblyincluding a belt and a vacuum port.

DETAILED DESCRIPTION

During a recoating process, a quantity of powder is deposited on one endof a build surface and then a recoater blade is pulled across thesurface at a set height above the previous build layer. As the blade ispulled across the surface, the powder is pushed in front of the bladeand only a thin layer of the powder is left behind after the bladepasses. The thickness of this layer is set by the height of the bladeabove the previously processed layer and may be in the range of about 20micrometers (µm) to 500 µm thick. However, the Inventors have recognizedthat one of the issues with using a solid blade recoating system is theinteraction between the previously printed layer and the recoater blade.In some cases, defects formed in a previously printed layer may protrudeup past the top of the nominal print height. If these defects extend upfar enough, the defects may contact the recoater blade as it travelsacross the next build plane. This contact between the recoater blade anddefects on a build surface may have different effects on the recoatingprocess and subsequent build layers including, but not limited to: layerdeformation, delamination and/or deformation of the printed part;pulling a printed part completely off a build plate; permanent damage tothe recoater blade such as a nick or cut in the blade; an upwardshifting of the entire blade to clear the defect; vibration of therecoater blade after passing the defect; and/or any other number ofdifferent types of effects that may occur due to the interaction of arecoater blade with a defect on a build surface. Depending on whetherthe recoater blade is made from a polymer or rubber material versus aharder metallic or ceramic blade, different effects may be more or lessprevalent. For example, a polymer or rubber recoater blades may be atless risk of catastrophic damage or delamination of the previouslyprinted part, but there is a much greater risk of damage such as cutsand nicks to the recoater blade which may cause uneven tracks in therecoated surface. Machine designs are possible that allow for easy orautomatic exchange of recoater blades when interference contact damageto the blade is detected. However, if the interference contact is stillpresent, the new blade may also be damaged.

While interference contact between a previously printed material and arecoater blade will not always cause a problem with subsequent printedlayers, the Inventors have recognized that in some cases an initialminor defect may cause a negative feedback where the defect grows insize over multiple subsequently deposited and fused layers such that asize of the growing defect may lead to large scale damage to therecoater or even failure of the entire print process. This type ofnegative feedback where each subsequent layer after an initial contactwith a defect produces a larger defect and corresponding increasedcontact with the recoater blade can cause complete process failure.Alternatively, this negative feedback can cause a part failure after thepart is complete. For example, if a layer of powder over a point issufficiently thick compared to the nominal recoating thickness, when thepoint is processed, there may not be sufficient laser power to fullymelt the layer in a solid weld to the previous layer. This weak point inthe part can delaminate during the part lifetime causing complete partfailure under load. Also this weak point may delaminate many layerslater during the print process causing large scale deformation of thepart and a complete print failure. This type of failure can also be veryhard to troubleshoot as the cause of the delamination and part failuremay be hundreds of layers separated from the actual failure point.

In view of the above, the Inventors have recognized the need for amethod to mitigate or reduce the likelihood of defects in a buildsurface growing in size during the formation of subsequent layers of apart. Accordingly, in some embodiments, a movable surface followingbehind a path of travel of a recoater blade, or moved over the buildsurface in a separate process, may induce a flow of fluid over the buildsurface by generating a boundary layer of the fluid on the movablesurface. Based on the type of powder (particle mass, particle density,particle size, etc.), there is a minimum velocity before a moving fluidwith a given density will start to have any effect on the powder. Belowthis velocity, the powder surface will not be substantially affected.Above this velocity, the moving fluid will start to entrain and move thepowder. By positioning the movable surface a fixed height above thenominal new powder level height, the established boundary layerthickness can be set such that it has little to substantially no effecton powder that is at or below the nominal layer thickness. However,areas of powder that extend above the nominal layer thickness may startto protrude into the boundary layer of flowing fluid over the buildsurface. Powder that extends far enough into the boundary layer above athreshold height above the build surface may be subject to a fluid flowvelocity that is at or above a minimum entrainment velocity of thepowder particles. At this point, the boundary layer may entrain at leasta portion, and in some instances substantially all, of the powderextending above the threshold height such that the entrained powder isremoved from the build surface at the defect location. This may reducethe excess powder layer thickness at the defect location. While some ofthe entrained powder may remain in the entrained boundary layer, anotherportion of the powder may be ejected from the boundary layer due tocentripetal forces. Depending on how the flow of fluid is handled, theentrained powder may either be removed from the system using a systemsuch as a filter or vacuum and/or the released powder may be spreadevenly over a much larger area than the initial area of excess powderthickness. In either case, this may drastically reduce the trend towardsa negative feedback loop resulting in a defect growing in size in anygiven spot or area during subsequent layer formation.

In view of the above, in one embodiment, a powder may be deposited ontothe build surface of a recoater assembly with a desired nominal layerthickness using a recoater assembly. In some instances, this may includepassing a recoater blade over the build surface to distribute the powderacross the build surface. A fluid may be flowed across at least aportion of the build surface, which may be behind a path of travel ofthe recoater blade across the build surface in some embodiments. Theflow of fluid may have a velocity profile that increases with increasingdistance from the build surface such that powder deposited onto thebuild surface above a threshold height from the build surface may becomeentrained in the flow of fluid. For example, in some embodiments, therecoater assembly may include a powder entrainment system with a movablesurface that may move relative to the underlying portion of the buildsurface. In instances where the powder entrainment system moves behind apath of travel of a recoater blade of the system, the moveable surfacemay move with a velocity relative to the build surface that is differentfrom a velocity of the recoater blade relative to the build surface. Ineither case, the velocity of the movable surface relative to theunderlying portion of the build surface may be sufficient to generate aboundary layer of the fluid to provide the desired velocity profile ofthe flow of fluid to entrain particles of the powder located above thethreshold height.

The methods and systems described herein may help to reduce the presenceof excess powder over discrete areas as well as over tracks that extendalong the length and/or width of a powder layer deposited onto a buildsurface of an additive manufacturing system. While in some embodimentsexcess powder may still be present on the surface, the excess powder maybe distributed over a much larger area and the maximum thickness at anyone point extending above the nominal thickness of a layer may besignificantly reduced. This reduction in peak areas may help to preventthe occurrence of a negative feedback loop resulting in defects on abuild surface growing in size during the deposition of subsequentlydeposited layers of material during a build process. This may result inboth increased part quality and fidelity as well as increasedoperational lifetimes for components such as the recoater blade of anadditive manufacturing system. Additionally, without wishing to be boundby theory, the larger the thickness of the initial excess powder height,the more effective the disclosed methods and systems become as thelarger the thickness, the more the powder will extend into the inducedboundary flow where the higher local gas velocity may result inincreased entrainment of the excess powder. Thus, the disclosed systemsbecome even more effective as the size of a defect and excess amounts ofpowder increase. However, embodiments in which the above-noted benefitsare not present and/or in which different benefits are present in anadditive manufacturing system implementing the methods and/or systemsdisclosed herein are also possible as the disclosure is not limited inthis fashion.

It should be understood that the methods and systems described hereinmay use any appropriate type of movable surface for generating a desiredboundary layer to provide a flow of fluid with a desired velocityprofile across at least a portion of a build surface of an additivemanufacturing system. For example, in some embodiments, a powderentrainment system may include a rotatable roller with at least aportion of a surface of the roller, e.g. the portion of the rollersurface oriented towards the build surface, disposed at a predeterminedheight above the build surface of an additive manufacturing system.Additionally, in some embodiments, an axis of rotation of the rotatableroller is parallel to the build surface. In another embodiment, thepowder entrainment system may include a belt that includes a portion ofthe belt with a surface that is oriented towards the build surface andthat is disposed at a predetermined height above the build surface of anadditive manufacturing system. Accordingly, the belt may be operatedsuch that the portion of the belt oriented towards and located proximateto the build surface may be moved relative to the build surface togenerate a desired flow of fluid across the build surface. In yetanother embodiment, a powder entrainment system may include a pluralityof rotatable disks located at a predetermined height above the buildsurface of an additive manufacturing system. In some instances, eachrotatable disc may have an axis of rotation that is angled relative tothe underlying build surface (e.g. orthogonal to the build surface).Accordingly, it should be understood that any appropriate componentcapable of being moved relative to an underlying build surface togenerate a boundary layer of fluid with a desired velocity profile toprovide the desired flow of fluid across an adjacent portion of thebuild surface may be used as the disclosure is not so limited.Additionally, depending on the specific embodiment, a movable surfaceproximate to the build surface used to generate the boundary layer offlowing fluid may either move in the same direction as a direction ofmotion of the overall powder entrainment system, a direction that isopposite the direction of motion of the powder entrainment system,and/or any other appropriate direction as the disclosure is not solimited.

As noted above, a minimum velocity of a fluid for entraining theparticles of a powder deposited onto a build surface may depend onvarious parameters such as the particle mass, particle density, particlesize, fluid density, and/or any other appropriate parameter. That said,in some embodiments, a minimum velocity for entraining the particles ofa powder in a flow of fluid, which may also correspond to a thresholdvelocity of a fluid flow at a threshold height from a build surface ofan additive manufacturing system, may be greater than or equal to 0.1meters per second (m/s), 0.2 m/s, 0.3 m/s, 0.4 m/s, 0.5 m/s, 1 m/s, 1.5m/s, and/or any other appropriate velocity. Correspondingly, the minimumentrainment velocity and/or threshold velocity of the flow of fluid maybe less than or equal to 2.0 m/s, 1.5 m/s, 1 m/s, 0.5 m/s, 0.4 m/s, 0.3m/s, and/or any other appropriate velocity. Combinations of theforegoing ranges are contemplated including, for example, a minimumentrainment velocity and/or threshold velocity of a flow of fluid for agiven type of powder may be between or equal to 0.1 m/s and 2.0 m/s.However, other combinations of the above ranges and/or velocities bothgreater than and less than those noted above are also contemplated asthe disclosure is not so limited. Additionally, the velocity of a fluidflow at different heights between a moving surface and a build surfacemay be measured in any appropriate manner including flow visualizationmethods; velocitometers; calculations and/or finite element analysistechniques based on the measured parameters of the fluid and theoperating parameters of the moveable surface for determining theboundary flow between the moveable surface and build surface; hot wireanemometers; ultrasonic flow sensors, and/or any other appropriatemethod.

To facilitate dispersing and/or removing powder particles located on abuild surface that extend above a threshold height above the buildsurface, a powder entrainment system may be configured to provide flowof fluid with a velocity profile that is greater than or equal to athreshold velocity, such as a minimum entrainment velocity of thepowder, at heights equal to or greater than the threshold height abovethe build surface in a direction parallel to a direction of gravity. Thethreshold height may be dependent on the nominal thickness of acorresponding powder layer and permitted layer thickness tolerancesdeposited on a build surface. Specifically, the build surface maycorrespond to a previously processed layer, a surface of a build plate,and/or any other appropriate surface that a powder layer to be processedis deposited on. Thus, the threshold height may be measured either fromthis build surface and/or from a nominal height of a powder layerdeposited onto the build surface. In either case, in some embodiments,the threshold height above a build surface may be greater than or equalto 25 µm, 30 µm, 40 µm 50 µm, 100 µm, 200 µm, and/or any otherappropriate height above the build surface. Correspondingly, thethreshold height may be less than or equal to 500 µm, 400 µm, 300 µm,200 µm, 100 µm, 50 µm, 20 µm, and/or any other appropriate height abovethe build surface. Combinations of the foregoing ranges are contemplatedincluding, for example, a threshold height that is between or equal to 5µm and 500 µm above the build surface may be used. Alternatively, thethreshold height may be measured from the nominal height of a powderlayer deposited onto the build surface. In such an embodiment, thethreshold height may be located at a height that is greater than orequal to 5 µm, 10 µm, 20 µm, 30 µm, 40 µm, 50 µm, 100 µm, and/or anyother appropriate height above the nominal height of the powder layerdisposed on the build surface. Correspondingly, the threshold height maybe located at a height that is less than or equal to 100 µm, 50 µm, 40µm, 30 µm, 20 µm, 10 µm, and/or any other appropriate height above thenominal height of the powder layer disposed on the build surface.Combinations of the foregoing are contemplated including, for example, athreshold height that is located at a height that is between or equal to5 µm and 100 µm above the nominal height of a layer of powder disposedon a build surface. Of course, depending on the specific layer thicknessand permitted tolerances, threshold heights both greater than and lessthan those noted above are contemplated as the disclosure is not limitedin this fashion.

It should be understood that any appropriate thickness of a powder layermay be used depending on the particular application. For example,appropriate thicknesses of powder layers sequentially deposited onto abuild surface may be greater than or equal to 20 µm, 30 µm, 40 µm, 50µm, 100 µm, 200 µm, 300 µm, and/or any other appropriate thickness.Correspondingly, the thickness of the sequentially deposited powderlayers may be less than or equal to 500 µm, 400 µm, 300 µm, 200 µm, 100µm, 50 µm, and/or any other appropriate thickness. Combinations of theforegoing are contemplated including, for example, a thickness of apowder layer deposited onto a build surface that is between or equal to20 µm and 500 µm. Of course thicknesses of a powder layer both greaterthan and less than those noted above are also contemplated as thedisclosure is not so limited.

In addition to the above, a portion of a movable surface that isoriented towards a build surface and used to generate the desired flowof fluid may be disposed within a predetermined height of the buildsurface. This may also be referred to as an offset between the buildsurface and the portion of the movable surface oriented towards thebuild surface. For example, a portion of the movable surface that isoriented towards a build surface and used to generate a flow of fluidparallel to the build surface may be disposed at a height from the buildsurface that is greater than or equal to 0.5 millimeters (mm), 1.0 mm,2.0 mm, 3.0 mm, 4.0 mm, 5.0 mm, and/or any other appropriate height.Correspondingly, the noted height may be less than or equal to 10.0 mm,9.0 mm, 8.0 mm, 7.0 mm, 6.0 mm, and/or any other appropriate height.Combinations of the foregoing ranges are contemplated including, forexample, a portion of a movable surface that is oriented towards thebuild surface may be located at a height over the underlying buildsurface that is between or equal to 0.5 mm and 10.0 mm. Of course, othercombinations of the above-noted ranges, as well as heights both greaterthan and less than those noted above, are also contemplated as thedisclosure is not limited in this fashion.

It should be understood that a recoater assembly along with thecorresponding recoater blade and powder entrainment system may betranslated across a build surface using any appropriate translationdirection, pattern, and/or velocity. For example, a recoater assemblymay be translated across at least a portion of a build surface with atranslational velocity parallel to the build surface that is greaterthan or equal to 5 mm/s, 10 mm/s, 20 mm/s, 50 mm/s, 100 mm/s, and/or anyother appropriate velocity. Correspondingly, a velocity of the recoaterassembly may be less than or equal to 200 mm/s, 150 mm/s, 100 mm/s, 50mm/s, and/or any other appropriate velocity. Combinations of theforegoing ranges are contemplated including, for example, a velocity ofthe recoater assembly in a direction that is parallel to the underlyingbuild surface that is between or equal to 5 mm/s and 200 mm/s, 25 mm secand 100 mm/sec, and/or any other appropriate combination of theforegoing ranges. Of course, velocities both greater than and less thanthose noted above are also contemplated as the disclosure is not solimited.

Various types of powders may be used in an additive manufacturing systemwhich may have a range of different types of characteristics dependingon the desired application. Possible powders may include, but are notlimited to, aluminum, titanium, steel, stainless steel, copper alloys,and/or any other appropriate type of material. Exemplary parameters ofthese powders are provided below. However, it should be understood thatthe disclosed methods and systems may be used with any appropriate typeof powder as the disclosure is not limited to only the types of powdersand powder characteristics described herein.

In some embodiments, a powder deposited onto a build surface of anadditive manufacturing system may have an average particle size measuredas the average maximum transverse dimension (e.g. average maximumdiameter) of the powder. Accordingly, in some embodiments, an averagemaximum transverse dimension of the particles of a powder may be greaterthan or equal to 5 µm, 10 µm, 15 µm, 20 µm, 30 µm, 40 µm, 50 µm, and/orany other appropriate size. Correspondingly, the average maximumtransverse dimension of the powder may be less than or equal to 100 µm,90 µm, 80 µm, 70 µm, 60 µm, 50 µm, and/or any other appropriate size.Combinations of the foregoing ranges are contemplated including, forexample, an average maximum transverse dimension of the particles of apowder that is between or equal to 5 µm and 100 µm, 15 µm and 50 µm ,and/or any other appropriate combination of the foregoing ranges. Ofcourse, powders with average sizes both greater than and less than thosenoted above are also contemplated as the disclosure is not so limited.Additionally, it should be understood that the average particle size(i.e. average maximum transverse dimension) may be measured using anyappropriate particle size analysis method including, but not limited to,particle size analyzers using static light scattering, laserdiffraction, staged sieving, , and/or any other appropriate method asthe disclosure is not so limited.

In some embodiments, a powder deposited onto a build surface of anadditive manufacturing system may be made from a material with a desireddensity. Depending on whether a polymeric or metal powder is used, theparticles of a powder may have a density that is greater than or equalto 1 g/cm³, 2 g/cm³, 2.6 g/cm³, 3 g/cm³, 4 g/cm³, 5 g/cm³, and/or anyother appropriate density. Correspondingly, the density of the particlesof a powder may be less than or equal to 9 g/cm³, 8.9 g/cm³, 8 g/cm³, 7g/cm³, 6 g/cm³, 5 g/cm³, and/or any other appropriate density.Combinations of the foregoing ranges are contemplated including, forexample, a density that is between or equal to 1 g/cm³ and 9 g/m³, 2.6g/cm³ and 8.9 g/cm³, and/or any other appropriate combination of theforegoing ranges. Of course, powders with particles having densitiesboth greater than and less than those noted above are also contemplatedas the disclosure is not so limited. In some embodiments, the density ofa powder may simply be known due to the material it is made from.Alternatively, appropriate methods of measuring the density of a powdermay include water displacement density measurements of the powder,though it should be understood that the disclosure is not limited to howthe density of a material is measured.

It should be understood that the additive manufacturing systemsdescribed herein may be operated using any appropriate type of fluidmedium that a build surface might be exposed to. For example, fornon-reactive materials that may be melted when exposed to oxygen (e.g.some polymers), the fluid may correspond to atmospheric air.Alternatively, the fluid may correspond to a relatively non-reactive gassuch as helium, argon, krypton, xenon, radon, nitrogen, and/or any otherappropriate gas depending on the intended application Additionally, anadditive manufacturing system may be operated using a fluid having anyappropriate pressure and/or density depending on the desired operatingcharacteristics of the system. That said, in some instances, an additivemanufacturing system may be operated using fluids with a pressure in arange between about 88 kPa and 102 kPa. However, embodiments in whichdifferent operating pressures are used including pressures both greaterand less than those noted above are also contemplated.

Depending on the particular embodiment, a recoater blade and/or aportion of a powder entrainment system that forms a movable surface forgenerating a boundary layer of fluid may be made out of any suitabletype of material including, for example, a metal, ceramic, plastic,and/or rubber. Accordingly, it should be understood that the variousembodiments disclosed herein are not limited to the specific types ofmaterials, or combinations materials, that the individual components aremade from.

For the sake of clarity, the embodiments described relative to thefigures illustrate powder entrainment systems that are moved togetherwith a recoater blade such that the powder entrainment system isdisposed behind and moves with the recoater blade in a direction oftravel of the recoater blade over a build surface. However, it should beunderstood that a powder entrainment system may also be mounted to asecondary motion mechanism that moves separately from the portion of therecoater assembly that the recoater blade is attached to. Thus, in someembodiments, a powder entrainment system may be moved separately fromthe recoater blade in any desired direction as the disclosure is notlimited in this fashion. Additionally, a powder entrainment system mayeither make a single pass over a recoated build surface, or it can bepassed over the recoated surface multiple times as the disclosure is notlimited to the number of times that a powder entrainment system ispassed over a build surface and/or the pattern in which it is traversedacross the build surface.

Turning to the figures, specific non-limiting embodiments are describedin further detail. It should be understood that the various systems,components, features, and methods described relative to theseembodiments may be used either individually and/or in any desiredcombination as the disclosure is not limited to only the specificembodiments described herein.

FIGS. 1A-1E show one embodiment of a prior art system that mayexperience negative feedback during the deposition and fusion ofsubsequent layers of powder 8 on a build surface 4 leading to the growthof a defect. Specifically, as shown in the figures, a printed layer mayproduce a defect 6 corresponding to a high spot where the fused materialextends upwards above the surrounding portions of the fused layersforming the build surface that each subsequent powder layer is depositedonto. This high spot can be caused by thermal stress and deformationthat has accumulated over several previous layers, or may be caused byother issues such as clumping of previous powder layers or weldingspatter from previous fused areas. If the defect is taller, i.e. extendsabove the nominal height, of the next layer, a recoater blade 2 of thesystem may contact the defect during translation of the recoater bladeacross the build surface. This interference contact between the recoaterblade and the defect during recoater motion may cause the recoater bladeto deform or deflect upward around the defect. This may result in morepowder 8 being deposited over the contact point. If the next printedlayer processes (i.e. melts) the powder over the previous high spot,this may result in a defect that extends even further above that printedlayer than the previous defect did over the corresponding printed layer.As subsequent layers are deposited and fused, this process may continueto repeat leading to larger defects and increased interference with therecoater blade. Ultimately, this process may continue either until therecoater blade is damaged beyond use, the previously printed layers aredamaged and deformed to a failure point, and/or until the recoatingprocess fails because the recoater mechanism jams at the interferencepoint between the defect and recoater blade.

In addition to the specific contact interference between a defect andthe recoater blade during powder deposition, the above-noted negativefeedback can also propagate from the initial interference contact pointto other portions of a build surface. Examples of different types ofdisturbances that may be formed in a powder layer deposited onto a buildsurface related to this contact interference is shown in FIGS. 2A-2D.FIG. 2A shows a top view of a recoater blade 2 translating towards adefect 6 located on a build surface on which a powder layer 8 has beendeposited. The defect is of an appropriate size such that contactbetween the recoater blade and the defect may occur during translationof the recoater blade. The interference between the recoater blade andthe defect may cause excessive powder thickness around the contact pointas well as in pockets 10 after the contact point if vertical vibrationsare induced in the recoater assembly as a result of the interferencecontact, see FIG. 2B. Alternatively, the contact may cause enough damageto the recoater blade such that a nick or chip is formed in the recoaterblade leading to the recoater blade forming a track 12 after the contactpoint where an increased amount of powder is deposited along the trackrelative to the surrounding portions of the build surface, see FIG. 2C.FIG. 2D shows how disturbances in the deposited powder layer may alsooccur across the width of the build plane as the contact between therecoater blade and one or more defects 6 may cause a vertical lifting ofthe entire recoater assembly. Subsequent vertical vibrations of therecoater blade may cause follow on tracks 12 that extend in a directionparallel to the recoater blade at a location on the build surface thatis located after the defect relative to a direction of travel of therecoater blade. Combinations of interference patterns from FIGS. 2B-2Dmay also be produced though it should be understood that potentialdefects and patterns formed in the deposited powder layer other thanthose described in the figures are also possible.

FIG. 3 depicts one embodiment of an additive manufacturing system 100.The additive manufacturing system 100 may include a build surface 102and a laser assembly 104. Depending on whether or not the manufacturingof a part has already commenced, the build surface 102 may include abuild plate, a portion of a printed part, a subsequently deposited andprocessed layer, and/or any other surface upon which a part or a portionof a part may be additively manufactured. The laser assembly 104 mayinclude an optics assembly 106 configured to emit one or more laserbeams 108 towards the build surface to melt powder disposed on the buildsurface in a desired pattern. Depending on the particular embodiment,the optics assembly may be movable relative to the build surface, thoughembodiments in which the lasers are scanned across the build surfaceusing galvanomirrors or other appropriate optical steering mechanismsare also contemplated. The additive manufacturing system may alsoinclude a recoater assembly 112 which may include a recoater blade 114and a powder entrainment system 116. As described previously, therecoater assembly may be translated in a direction across at least aportion of a build surface during a powder recoating process. Aselaborated on below, the powder entrainment system may follow behind apath of travel of the recoater blade though embodiments in which thepowder entrainment system is translated across the build surfaceseparately from the recoater blade are also contemplated.

In the depicted embodiment, the powder entrainment system 116 includes aspinning rod disposed behind a path of travel of the recoater blade 114.The rod has an axis of rotation that is substantially parallel to theunderlying build surface 102 such that the spinning motion of the rodinduces a boundary flow around the rod where at least a portion of theboundary flow is disposed between the rod, or other movable surface of apowder entrainment system, and the build surface. By changing therotational velocity, the radius of the rod, and the height of therotating rod above the new powder level, the shape and magnitude of theboundary layer relative to the underlying layer of powder can becontrolled to disperse and/or remove powder located at a height greaterthan a threshold height above the build surface which may correspond toa previously deposited and processed layer and/or an underlying buildplate.

In some embodiments, an additive manufacturing system may additionallyinclude a processor 110 which may include an associated memoryconfigured to store processor-executable instructions to perform themethods described herein. The processor 110 may be operatively coupledto the laser assembly 104, the recoater assembly 112 and any componentstherein, including but not limited to the optics assembly 110, thepowder entrainment system, and/or any other appropriate component of theadditive manufacturing system. Accordingly, the processor may operateany desired components of the additive manufacturing system to performthe methods described herein.

FIG. 4 is a schematic representation of an additive manufacturing system100, according to some embodiments. In the depicted embodiment, theadditive manufacturing system 100 includes a build surface 102, foursupport columns 118, two support rails 120, a recoater assembly 112. Therecoater assembly may include a recoater support 122, a recoater bladehousing 124, a recoater blade 114, and a powder entrainment system 116as well as a build surface 120. The four support columns and two supportrails support the recoater assembly at a desired height and orientationabove the build surface. The two support rails 104 may be connected tothe four support columns 102. In particular, each of the two supportrails is connected to two of the four support columns 102 in a directionthat is parallel to the depicted X axis. In some embodiments, thesupport rails 104 are coupled to the support columns 102 viatranslational attachments 126. Thus, the translational attachments mayallow ends of each support rail to translate vertically (i.e., in adirection parallel to the Z axis) along the support columns 102 to allowa height of the support rails and the associated recoater assembly to becontrolled using any appropriate arrangement of actuators, not depicted.

As noted above, the recoater assembly 112 includes a recoater support122, a recoater blade housing 124, a recoater blade 114, and a powderentrainment system 116. The recoater blade housing may be configured tosecurely hold the recoater blade, and may be mounted to the recoatersupport. Similarly, in some embodiments, a powder entrainment system 116may be mounted to the recoater blade housing, or other appropriateportion of the recoater assembly, such that the powder entrainmentsystem may be translated with the recoater assembly across the buildsurface 102. In the depicted embodiment, the powder entrainment systemcorresponds to a rotatable cylinder with an axis of rotation that it isoriented in a direction that is parallel to the underlying buildsurface. The rotatable cylinder, or other moveable surface of a powderentrainment system, may be driven using any appropriate actuator 116 aconfigured to drive the moveable surface in a desired direction. Therecoater support may be coupled to the support rails 120. In thedepicted embodiment, the recoater support extends between the supportrails along an axis parallel to the Y axis and perpendicular to the Xaxis. In particular, the recoater support is coupled to the supportrails via recoater translational attachments 128 disposed at either endof the recoater support. This may allow the recoater support, and thus,the overall recoater assembly to translate horizontally across the buildsurface in a direction that is parallel to the build surface and the Xaxis along the support rails 104 using any appropriate type ofassociated actuator, not depicted.

Depending on the particular embodiment, a distance between a recoaterand a build surface may be measured and/or controlled via any suitabletypes of measurement or control systems. For example, vertical motion ofa recoater assembly (e.g., along support columns 118) may be driven byactuators such as ball screw driven stages, linear motor stages, linearactuators, pneumatic actuators, hydraulic actuators, and so on.Moreover, the position of such vertical motion stages may be trackedand/or measured via systems such as rotary encoders on ball screws,linear optical encoders, LVDT sensors, laser displacement sensors, andso on. For example, in one embodiment, a vertical motion stage may bedriven by a ball screw driven linear actuator, and the position of themotion stage may be tracked via linear optical encoders. Of course, itshould be appreciated that the current disclosure is not limited to anyparticular combination of types of vertical motion stages and/or systemsfor tracking or measuring the position of the motion vertical motionstages. Similarly, the systems disclosed herein may include any suitabletypes of motion stages for accommodating movement of the recoaterassembly along the support rails. For example, the recoater assembly maybe driven along the support rails via ball screw driven linear slides,belt driven linear actuators, pneumatic actuators, hydraulic actuators,and so on, and the position of the recoater assembly may be monitoredvia one or more of rotary encoders, linear optical encoders, LVDTsensors, laser displacement sensors, and so on.

As discussed previously, in some embodiments, an additive manufacturingsystem 100 may include a processor 110 that is operatively coupled tothe recoater assembly to control operation of powder dispensing,vertical and/or horizontal translation of the recoater assembly 112,and/or operation of the powder entrainment system 116. For example, theprocessor may be operatively coupled to one or more actuators associatedwith one or more of the attachments 126 and/or 128, and the processormay control operation of each actuator to control a height of therecoater assembly relative to the build surface and/or motion of therecoater assembly across at least a portion of the build surface.Additionally, the processor may be operatively coupled to the powderentrainment system and may be configured to control operation of thepowder entrainment system using any of the methods disclosed herein tomitigate the formation of defects extending above a nominal height of apowder layer disposed on the build surface 102.

FIG. 5 depicts a schematic embodiment of a powder layer 130 depositedonto a build surface 102. The recoater blade of the recoater assembly isdragged across the surface of the build plate leaving a desiredthickness of the powder layer behind a path of travel of the recoaterblade. Correspondingly, a pile of powder 132 may build up on a frontsurface of the recoater blade relative to the direction of travel as therecoater blade is dragged across the build surface. The recoater systemmay also include a powder entrainment system 116 in the form of arotatable cylinder, or other appropriate moveable surface that may bemoved relative to the underlying build surface to induce a boundary flowadhered to the movable surface that may provide a flow of fluid betweenthe movable surface and the build surface. For example, the rotatablecylinder may be rotated relative to the build surface with a rotationalvelocity “w” in either direction. Depending on the radius of thecylinder and the rotational speed of the cylinder, a boundary flow maybe induced on the cylinder with any desired boundary layer height H_(B)and velocity profile 134, see FIG. 6 . This boundary layer of fluidadhered to the surface of the rotating cylinder, or other movablesurface of a powder entrainment system, may result in a flow of fluidbetween the build surface and a surface of the cylinder, or othermovable surface of a powder entrainment system, oriented towards thebuild surface. Further, since the rotating rod may be located at aheight well above the nominal new powder layer thickness, even defectsfrom a previous print layer that may contact the recoater blade maystill be well below the solid surface of the rotating rod so no contactbetween the defect and the rod may occur. Accordingly, as elaborated onbelow, this method may help to remove and/or disperse at least aportion, a majority, and in some instances substantially all of theexcess powder deposited at a location of a defect which may help tolimit the maximum height of excess powder deposited in a location whichmay reduce the risk of a negative feedback loop causing print problemsduring an additive manufacturing process.

As shown in FIG. 7 , a rotatable cylinder forming a portion of a powderentrainment system 116 may be used to disperse and/or remove any excesspowder of a powder layer 130 that extends far enough into the boundarylayer around the spinning rod. Specifically, the velocity profile 134 ofthe boundary flow may increase in velocity from the build surface 102towards the movable surface of the cylinder or other appropriatemoveable surface oriented towards the build surface used to induce theflow of fluid. In the figure, a powder layer 130 has been deposited ontothe build surface with a nominal layer height of H_(N) and a permittedlayer height tolerance H_(t) that the powder layer may extend above thenominal layer height. Correspondingly, a threshold height above thebuild surface above which the powder may be dispersed and/or removed maycorrespond to H_(Th) which is the combined total of the nominal layerheight and layer height tolerance. Correspondingly, an outer surface ofthe rotating cylinder oriented towards the build surface may be offsetfrom the build surface by an offset height Ho. By selecting anappropriate combination of the cylinder size and rotational velocity,the velocity profile of the boundary flow may have a velocity that isequal to or greater than a minimum entrainment velocity of the powder ofthe powder layer at heights above the build surface that are greaterthan or equal to the threshold height. Accordingly, any excess powderthat extends to a height greater than the threshold height relative tothe build surface may either be removed and/or distributed over a muchlarger area due to the powder located at or above the threshold heightbeing entrained in the flow of fluid while leaving the powder below thethreshold height in the powder layer in a substantially undisturbedstate.

In some embodiments, it may be desirable to either increase theturbulence within a boundary flow adhered to a movable surface of apowder entrainment system and/or to provide pulsatile flow. Accordingly,while a solid smooth surface such as a solid rotating rod is depicted inother embodiments as illustrated in FIG. 8 , in some embodiments amovable surface of a powder entrainment system 116 used to induce aboundary flow may include a plurality of surface features disposedthereon. For example, in the depicted embodiment of a rotating cylinder,the rotating cylinder may include a plurality of surface features 117with varying heights disposed on the surface. Specifically, surfacefeatures such as fins, protrusions, bumps, divots, dimples, channels,and/or any other appropriate surface future may be provided on a movablesurface to provide a desired pattern of flow. While such a feature maybe optional, these types of surface features may entrain more flowand/or add pressure variations (i.e. flow pulses) to the entrained flowwhich may aid in randomly dispersing excess powder on a build surface ofa system and/or increasing the size of an induced boundary layer offluid attached to the movable surface.

Depending on whether or not a movable surface used to induce a boundaryflow between a powder entrainment system 116 and a build surface movesin a direction that is the same or opposite from a direction of travelof the overall powder entrainment system, the resulting velocity profile134 of the boundary layer may have a different shape. Specifically, asshown in FIG. 9 having a moving surface that moves in a directionopposite the direction of travel of the overall powder entrainmentsystem results in a boundary flow with a velocity profile that initiallyincreases in velocity in a direction oriented towards the movablesurface prior to decreasing in velocity. Without wishing to be bound bytheory, this is due to the first velocity profile 134 a from rotation ofthe rod and the second velocity profile 134 b from translation of thepowder entrainment system over the build surface at least partiallycanceling each other out. Correspondingly, when the movable surface ofthe powder entrainment system moves in the same direction as thedirection of movement of the overall powder entrainment system, thevelocity profiles are constructive such that the overall velocityprofile 134 increases continuously in a direction oriented towards themovable surface of the depicted rotating cylinder, see FIG. 10 .However, in general the translational speed of the powder entrainmentsystem may be significantly slower than the relative velocity of themovable surface relative to the underlying build surface such that therelative directions of the overall translation of the system anddirection of movement of the movable surface relative to the overallsystem may have little effect on the net boundary layer velocity profileshape.

In some instances, it may be desirable to strip a portion of a boundarylayer and the entrained powder from a movable surface to help disperseand/or remove the entrained powder. For example, as shown in FIG. 11 , amask 138 may be positioned adjacent to the movable surface of a powderentrainment system 116 such as the depicted rotating cylinder. The maskmay correspond to a structure that is contoured to at least a portion ofthe movable surface and may be disposed adjacent to the movable surfaceat a distance that is less than a thickness of the induced boundary flowattached to the movable surface. Accordingly, the mask may cause atleast a portion of the boundary flow to be detached from the movablesurface. While the mask has been depicted as being positioned on aleading edge of the rotatable cylinder relative to the indicateddirection of motion, embodiments in which the mask is disposed on both aleading and/or trailing portions of a movable surface of a powderentrainment system are also contemplated, see FIGS. 12 and 13 . Ineither case, the mask may serve to strip the boundary layer flow fromthe movable surface at a location close to entrainment point to eithercreate a new fresh boundary layer close to the entrainment point or tostrip the majority of the entrained flow after the entrainment point. Insome embodiments, the mask, or other portion of the powder entrainmentsystem or recoater assembly, may also be fitted with a vacuum port 140connected to an appropriate vacuum source, not depicted. In the depictedembodiment, the vacuum port is oriented towards a location where themask strips the boundary layer off of the movable surface though otherarrangements are also contemplated. The use of a vacuum port may help tocapture and remove at least a portion of the entrained powder which mayreduce the quantity of a powder that is redeposited onto the buildsurface.

While a rotatable cylinder has been depicted in the above embodiments,it should be understood that a rotatable cylinder is only one way ofimplementing a movable surface to induce a flow of fluid over the buildsurface of an additive manufacturing system. Other exemplary types ofsystems that may function as the movable surface of a powder entrainmentsystem are elaborated on below. Accordingly, it should be understoodthat the current disclosure is not limited to any specific constructionto induce a flow of fluid between a recoater assembly and a buildsurface to entrain powder particles located above a threshold heightrelative to the underlying build surface.

FIGS. 14-16 depict another embodiment of a recoater assembly 112 with apowder entrainment system 116. In the depicted embodiment, the recoaterassembly includes a recoater blade 114 that traverses a build surface,not depicted, in a desired direction. The powder entrainment system 116includes a plurality of rotatable disks 142 that are arranged in anarray that extends along at least a portion of a length, and in someinstances substantially all of the length, of the recoater blade. Eachof the rotatable disks includes an axis of rotation that extends in adirection that is angled relative to the underlying build surface, suchas in a direction that is perpendicular to the build surface.Accordingly, a bottom surface of each of the rotatable disks may besubstantially parallel to the underlying build surface. By driving eachof the disks to rotate about their rotational axes using one or moreappropriate actuators, not depicted, the bottom surface of the disksoriented towards the build surface will rotate relative to the buildsurface which may induce a boundary flow of fluid between the rotatingdisks surfaces and the build surface in a manner similar to thatdescribed above though the relative speed of the boundary layer will begreatest at the outer most edge of the disks due to the translationalspeed of each point on the surfaces increasing with increasing radius.Accordingly, the induced flow between the disk and nominal powder layercan be used in order to entrain powders deposited at heights greaterthan a threshold height from a build surface in a manner similar to thatnoted above. Depending on the particular design, the disks can bearranged in straight arrays including one or more aligned rows of diskswith minimal gaps between disks, see FIG. 15 . Alternatively, the disksmay be set in staggered arrays where separate rows of the disks may beoffset from one another such that the disks in one row may overlap withgaps in an adjacent row which may result in every point in the powderlayer being subject to at least two different flow conditions on eachpass of the powder entrainment system, see FIG. 16 .

FIGS. 17-18 depict yet another embodiment of recoater assembly 112including a powder entrainment system 116 with a movable surface thatmay be used to induce a boundary flow of fluid between a build surface102 and a portion of a movable surface oriented towards the buildsurface. In this embodiment, the movable surface corresponds to a belt144 that includes at least a portion that is positioned proximate toand/or oriented towards the build surface within an appropriate offsetdistance from the build surface as previously discussed. Similar to theabove embodiments, the belt is located behind the recoater blade 114relative to a path of travel of the recoater blade across the buildsurface. The belt may be associated with two or more rollers 146 whichare arranged to guide the belt through a desired path of travel. Therollers may either be the same size and/or different sizes depending onthe desired application. At least one of the rollers may be a driveroller with an associated actuator, not depicted, that is used to drivethe belt in a desired direction relative to the underlying buildsurface. In the embodiment shown in FIG. 17 two rollers are positionedproximate to the build surface such that a portion of the belt extendsin a direction substantially parallel to the underlying build surfacefor a predetermined length. Such an embodiment may be advantageous inthat the boundary flow adhered to the moving belt may be applied over abroad area of the build surface. Alternatively, a single roller may belocated proximate to the build surface such that the belt moves over aregion of the build surface as it moves over the roller proximate to thebuild surface, see FIG. 18 . This may cause the boundary flow attachedto the belt to be applied over a smaller area corresponding to theportion of the roller oriented towards the build surface. Depending onthe overall radius of the roller and corresponding thickness of theboundary layer, this may cause the boundary flow to apply flows of fluidwith velocities above the minimum entrainment velocity of the powderover a relatively small portion of the build surface. As also depictedin the embodiment of FIG. 18 , in some instances a vacuum port and/ormask, such as the combined mask and vacuum port 138/140 may bepositioned proximate to a portion of the belt downstream from a locationwhere the belt moves over the build surface relative to a direction offlow across the build surface. As discussed above, this may help tostrip off and/or remove the boundary flow and entrained powder from themoving belt.

The above-described embodiments of the technology described herein canbe implemented in any of numerous ways. For example, the embodiments maybe implemented using hardware, software or a combination thereof. Whenimplemented in software, the software code can be executed on anysuitable processor or collection of processors, whether provided in asingle computing device or distributed among multiple computing devices.Such processors may be implemented as integrated circuits, with one ormore processors in an integrated circuit component, includingcommercially available integrated circuit components known in the art bynames such as CPU chips, GPU chips, microprocessor, microcontroller, orco-processor. Alternatively, a processor may be implemented in customcircuitry, such as an ASIC, or semicustom circuitry resulting fromconfiguring a programmable logic device. As yet a further alternative, aprocessor may be a portion of a larger circuit or semiconductor device,whether commercially available, semi-custom or custom. As a specificexample, some commercially available microprocessors have multiple coressuch that one or a subset of those cores may constitute a processor.Though, a processor may be implemented using circuitry in any suitableformat.

Further, it should be appreciated that a computing device may beembodied in any of a number of forms, such as a rack-mounted computer, adesktop computer, a laptop computer, or a tablet computer. Additionally,a computing device may be embedded in a device not generally regarded asa computing device but with suitable processing capabilities, includinga Personal Digital Assistant (PDA), a smart phone, tablet, or any othersuitable portable or fixed electronic device.

Also, a computing device may have one or more input and output devices.These devices can be used, among other things, to present a userinterface. Examples of output devices that can be used to provide a userinterface include display screens for visual presentation of output andspeakers or other sound generating devices for audible presentation ofoutput. Examples of input devices that can be used for a user interfaceinclude keyboards, individual buttons, and pointing devices, such asmice, touch pads, and digitizing tablets. As another example, acomputing device may receive input information through speechrecognition or in other audible format.

Such computing devices may be interconnected by one or more networks inany suitable form, including as a local area network or a wide areanetwork, such as an enterprise network or the Internet. Such networksmay be based on any suitable technology and may operate according to anysuitable protocol and may include wireless networks, wired networks orfiber optic networks.

Also, the various methods or processes outlined herein may be coded assoftware that is executable on one or more processors that employ anyone of a variety of operating systems or platforms. Additionally, suchsoftware may be written using any of a number of suitable programminglanguages and/or programming or scripting tools, and also may becompiled as executable machine language code or intermediate code thatis executed on a framework or virtual machine.

In this respect, the embodiments described herein may be embodied as aprocessor readable storage medium (or multiple computer readable media)(e.g., a computer memory, one or more floppy disks, compact disks (CD),optical disks, digital video disks (DVD), magnetic tapes, flashmemories, RAM, ROM, EEPROM, circuit configurations in Field ProgrammableGate Arrays or other semiconductor devices, or other tangible computerstorage medium) encoded with one or more programs that, when executed onone or more processors, perform methods that implement the variousembodiments discussed above. As is apparent from the foregoing examples,a processor readable storage medium may retain information for asufficient time to provide computer-executable instructions in anon-transitory form. Such a processor readable storage medium or mediacan be transportable, such that the program or programs stored thereoncan be loaded onto one or more different computing devices or otherprocessors to implement various aspects of the present disclosure asdiscussed above. As used herein, the term “processor-readable storagemedium” encompasses only a non-transitory processor-readable medium thatcan be considered to be a manufacture (i.e., article of manufacture) ora machine. Alternatively or additionally, the disclosure may be embodiedas a processor readable medium other than a processor-readable storagemedium, such as a propagating signal.

The terms “program” or “software” are used herein in a generic sense torefer to any type of computer code or set of computer-executableinstructions that can be employed to program a computing device or otherprocessor to implement various aspects of the present disclosure asdiscussed above. Additionally, it should be appreciated that accordingto one aspect of this embodiment, one or more computer programs thatwhen executed perform methods of the present disclosure need not resideon a single computing device or processor, but may be distributed in amodular fashion amongst a number of different computers or processors toimplement various aspects of the present disclosure.

Processor-executable instructions may be in many forms, such as programmodules, executed by one or more processors. Generally, program modulesinclude routines, programs, objects, components, data structures, etc.that perform particular tasks or implement particular abstract datatypes. Typically the functionality of the program modules may becombined or distributed as desired in various embodiments.

The embodiments described herein may be embodied as a method, of whichan example has been provided. The acts performed as part of the methodmay be ordered in any suitable way. Accordingly, embodiments may beconstructed in which acts are performed in an order different thanillustrated, which may include performing some acts simultaneously, eventhough shown as sequential acts in illustrative embodiments.

While the present teachings have been described in conjunction withvarious embodiments and examples, it is not intended that the presentteachings be limited to such embodiments or examples. On the contrary,the present teachings encompass various alternatives, modifications, andequivalents, as will be appreciated by those of skill in the art.Accordingly, the foregoing description and drawings are by way ofexample only.

What is claimed is:
 1. A method of recoating a build surface of anadditive manufacturing system, the method comprising: depositing powderonto the build surface with a recoater assembly; and flowing a fluidacross at least a portion of the build surface with a velocity profilethat increases with increasing distance from the build surface, andentraining powder above a threshold height from the build surface in theflow of fluid.
 2. The method of claim 1, wherein flowing the fluidacross the build surface includes flowing the fluid across the buildsurface behind a path of travel of the recoater blade.
 3. The method ofclaim 1, wherein a velocity of at least a portion of the flow of fluidis between or equal to 0.1 meters per second (m/s) and 2.0 m/s at aheight from the build surface that is between or equal to 0.5millimeters (mm) and 10.0 mm.
 4. The method of claim 1, furthercomprising generating the flow of fluid by moving a movable surfacerelative to the build surface.
 5. The method of claim 4, wherein aportion of the movable surface oriented towards the build surface movesin a direction of motion of the recoater blade.
 6. The method of claim4, wherein a portion of the movable surface oriented towards the buildsurface moves in a direction that is opposite a direction of motion ofthe recoater blade.
 7. The method of claim 4, wherein a plurality ofsurface features with varying heights are disposed on the movablesurface.
 8. The method of claim 4, further comprising disrupting aboundary layer of the fluid adhered to the movable surface.
 9. Themethod of claim 8, wherein disrupting the boundary layer of the fluidcomprises disrupting the boundary layer using a mask.
 10. The method ofclaim 9, wherein the mask is contoured to at least a portion of themovable surface.
 11. The method of claim 9, wherein the mask is disposedadjacent to the movable surface at a distance that is less than athickness of the boundary layer of the fluid adhered to the movablesurface.
 12. The method of claim 4, wherein moving the movable surfacecomprises rotating a rotatable roller about an axis of rotation of therotatable roller that is parallel to the build surface.
 13. The methodof claim 4, wherein moving the movable surface comprises moving a belt,and wherein moving belt includes moving at least a portion of the beltparallel to the build surface.
 14. The method of claim 4, herein movingthe movable surface comprises rotating a plurality of rotatable disks.15. The method of claim 14, wherein the plurality of rotatable disks isarranged in an array.
 16. The method of claim 1, further comprisingremoving powder entrained in the fluid from the additive manufacturingsystem.
 17. A method of recoating a build surface of an additivemanufacturing system, the method comprising: moving a recoater bladeacross a layer of powder deposited on a build surface of the additivemanufacturing system; trailing a powder entrainment system behind therecoater blade relative to a direction of the recoater blade across thebuild surface; and moving a movable surface of the powder entrainmentsystem relative to a proximate portion of the build surface at a firstvelocity that is different from a second velocity of the recoater bladerelative to the build surface.
 18. The method of claim 17, wherein thefirst velocity is between or equal to 0.1 meters per second (m/s) and2.0 m/s, and wherein at least a portion of the movable surface isdisposed at a height from the build surface that is between or equal to0.5 millimeters (mm) and 10.0 mm.
 19. The method of claim 17, furthercomprising moving a portion of the movable surface oriented towards thebuild surface in the direction of motion of the recoater blade.
 20. Themethod of claim 17, further comprising moving a portion of the movablesurface oriented towards the build surface in a direction that isopposite to the direction of motion of the recoater blade.
 21. Themethod of claim 17, wherein a plurality of surface features with varyingheights are disposed on the movable surface.
 22. The method of claim 17,further comprising disrupting a boundary layer of the fluid adhered tothe movable surface.
 23. The method of claim 17, wherein moving themovable surface comprises rotating a rotatable roller about an axis ofrotation of the rotatable roller that is parallel to the build surface.24. The method of claim 17, wherein moving the movable surface comprisesmoving a belt, and wherein moving belt includes moving at least aportion of the belt parallel to the build surface.
 25. The method ofclaim 17, wherein moving the movable surface comprises rotating aplurality of rotatable disks.
 26. The method of claim 25, wherein theplurality of rotatable disks is arranged in an array.